Exhaust gas systems consisting of an exhaust gas pipe for discharging an exhaust gas stream emerging from a diesel engine and a heat shield in the form of a tubular cover arranged spacedly, on the outside of the exhaust gas pipe, are known inter alia from the 6030 Series agricultural tractors made by John Deere.
The exhaust gas standards enacted by the European Union provide for a gradual reduction in the soot particles produced by diesel engines and discharged into the environment with the engine exhaust gas. Soot particle discharge is restricted by using soot particle filters, as a rule with “wall-flow filters,” in which the engine exhaust gas passes through a porous filter wall of a ceramic or metallic material. As a result, the soot particles contained in the engine exhaust gas become deposited both on the surface of and also inside the filter wall such that the exhaust gas back-pressure increases as the degree of clogging of the filter wall increases. To regenerate the soot particle filter, the deposited soot particles are burned at regular intervals, for which purpose the temperature of the engine exhaust gas is increased from time to time to temperatures of over 500° C., for example by means of an oxidation catalytic converter connected upstream of the soot particle filter. During regeneration, correspondingly high exhaust gas temperatures may occur at the exhaust tail pipe of the exhaust gas system, which lead under certain circumstances to the formation of undesirable nitrogen oxides.
Against this background, WO 2008/060559 A2 discloses a device for reducing the exhaust gas temperature at an exhaust tail pipe. The device, which may be fitted to the exhaust tail pipe by means of a clip or clamp, comprises a nozzle, which is fitted by means of a plurality of radially arranged holding struts in such a way on an adjoining diverter housing that, on passage of the exhaust gas stream, a partial vacuum for drawing in cooler ambient air may be produced in an inlet formed between the nozzle and the diverter housing. However, the shape of the nozzle or of the diverter housing, which shape tapers in the passage direction of the exhaust gas stream, leads to an undesired increase in the exhaust gas back-pressure in the exhaust gas system.
It is therefore the object of the present invention to provide a device of the above-mentioned type which enables cooling of an exhaust gas stream emerging in particular from a diesel particle filter without undesirably increasing the exhaust gas back-pressure in the region of an exhaust tail pipe.